// 抽象类UserTest
public abstract class UserTest
{
    // 三个抽象方法
    public abstract void M1();
    public abstract void M2();
    public abstract void M3();
}

// 子类继承并实现抽象方法
public class UserTestImpl : UserTest
{
    public override void M1()
    {
        Console.WriteLine("子类实现M1方法");
    }

    public override void M2()
    {
        Console.WriteLine("子类实现M2方法");
    }

    public override void M3()
    {
        Console.WriteLine("子类实现M3方法");
    }
}